Search for the Decay $\tau^{-}\to 4pi^{-}3\pi^{+}(\pi^{0})\nu_{\tau}$

TL;DR

This paper reports a search for a rare tau decay into seven charged pions with or without a neutral pion, setting a new upper limit on its branching fraction using data from the CLEO II detector.

Contribution

The study provides the first stringent upper limit on the branching fraction of tau decaying into seven charged pions, improving previous constraints.

Findings

No evidence for the decay was observed.

An upper limit on the branching fraction was set at 2.4 x 10^(-6).

The result significantly improves previous limits.

Abstract

We have searched for the decay of the tau lepton into seven charged particles and zero or one pi0. The data used in the search were collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 4.61 fb^(-1). No evidence for a signal is found. Assuming all the charged particles are pions, we set an upper limit on the branching fraction, B(tau- -> 4pi- 3pi+ (pi0) nu_tau) < 2.4 x 10^(-6) at the 90% confidence level. This limit represents a significant improvement over the previous limit.